1. Technical Field of the Invention
The present invention relates to an industrial salt obtained from combustion gas exhausted from a cement kiln composing a cement burning facility, and an apparatus and a method for manufacturing the industrial salt.
2. Description of the Related Art
It is noticed that chlorine, sulfur, alkali and the like cause troubles such as preheater clogging in cement manufacturing facilities, and especially chlorine has the most harmful effect, so that cement kiln chlorine bypass systems have been used in order to remove chlorine by extracting a part of combustion gas from a kiln exhaust gas passage, which runs from an inlet end of a cement kiln to a bottom cyclone.
In this chlorine bypass system, more chlorine is distributed on fine powder side of the dust, which is generated by cooling the extracted exhaust gas, so that the dust is separated into coarse powder and fine powder by a classifier, the coarse powder is returned to a cement kiln system, and the fine powder (chlorine bypass dust) containing separated potassium chloride and the like is recovered, and is added to a cement grinding mill system (as exemplarily described in Patent Document 1).
However, in recent years, recycling of waste through conversion to cement raw material or fuel has been promoted, which increases the quantity of volatile matters such as chlorine, sulfur and alkali and the quantity of chlorine bypass dust generated as the quantity of the treated waste increases. As a result, all of the chlorine bypass dust cannot be utilized in a cement grinding process, so that the chlorine bypass dust is subject to washing treatment, however, it is anticipated that the quantity of chlorine bypass dust generated will further increase, which necessitates developments of methods for effectively utilizing the dust.
From the above-mentioned point of view, in a method of converting to cement raw material described in Patent Document 2, to wastes containing chlorine such as waste refuse incineration fly ash and chlorine bypass dust is added water to allow the chlorine in the wastes to be eluted and filtrated; desalted cake obtained is utilized as a cement raw material; and wastewater is purified and is discharged as it is or salt is recovered from the wastewater, which makes it possible to effectively utilize the wastes without causing environmental pollution.
In addition, in Patent Documents 3 and 4 is described a method for recovering industrial salt from combustion exhaust gas discharged from cement kilns. As shown in FIG. 2(b), in this method, dust (chlorine bypass dust) contained in a part of combustion gas extracted from a cement kiln combustion gas is collected; the chlorine bypass dust is washed so as to be separated into cake and filtrate; from the separated filtrate is removed heavy metals; from treated water is removed calcium components; the treated water is separated into concentrated salt water and desalted water through an electrodeposition device; and finally from the concentrated salt water is recovered industrial salt including alkali metal salt through crystallization.